Simplify stack-allocated Lisp objects, and make them more portable.

The build_local_string macro was used in two ways: (1) string
literals for which scoped allocation suffices, and (2) file name
components, where it's not safe in general to assume bounded-size
ASCII data.  Simplify by defining a new macro SCOPED_STRING that
allocates a block-scope string, and by using SCOPED_STRING for (1)
and build_string for (2).  Furthermore, actually use stack
allocation only for objects known to have sufficient alignment.
This simpler implementation means Emacs can make
USE_STACK_LISP_OBJECTS the default unless GC_MARK_STACK !=
GC_MAKE_GCPROS_NOOPS.
* lisp.h (GCALIGNED): Align even if !USE_STACK_LISP_OBJECTS,
for fewer differences among implementations.
(struct Lisp_String): Now GCALIGNED.
(USE_STACK_LISP_OBJECTS): Default to true, since the
implementation no longer insists on a nonempty GCALIGNED.
But make it false if GC_MARK_STACK != GC_MAKE_GCPROS_NOOPS.
(SCOPED_CONS_INITIALIZER): Remove, since it's no longer needed
separately.  Move definiens to scoped_cons.  The old definition
was incorrect when GCALIGNED was defined to be empty.
(union Aligned_String): New type.
(USE_STACK_CONS, USE_STACK_STRING): New constants, so that the
implementation ports to compilers that don't align strictly enough.
Don't worry about the union sizes; it's not worth bothering about.
(scoped_cons, scoped_list1, scoped_list3, scoped_list4):
Rewrite using USE_STACK_CONS.
(scoped_cons): Assume the use of union Aligned_Cons.
(lisp_string_size, make_local_string, build_local_string): Remove.
Unless otherwise specified, all callers of build_local_string
changed to use SCOPED_STRING.
(SCOPED_STRING): New macro.
* data.c (wrong_choice):
* menu.c (single_menu_item):
* process.c (Fformat_network_address):
Hoist use of SCOPED_STRING out of a scope, so that its returned
object lives long enough.
* fileio.c (Fexpand_file_name): Use build_string, not SCOPED_STRING,
as the string might be long or might not be ASCII.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/emacs.c b/src/emacs.c
index 241479fecf2..3c31827e994 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -423,7 +423,7 @@ init_cmdargs (int argc, char **argv, int skip_args, char *original_pwd)
      if it would otherwise be treated as magic.  */
   handler = Ffind_file_name_handler (raw_name, Qt);
   if (! NILP (handler))
-    raw_name = concat2 (build_local_string ("/:"), raw_name);
+    raw_name = concat2 (SCOPED_STRING ("/:"), raw_name);
 
   Vinvocation_name = Ffile_name_nondirectory (raw_name);
   Vinvocation_directory = Ffile_name_directory (raw_name);
@@ -441,7 +441,7 @@ init_cmdargs (int argc, char **argv, int skip_args, char *original_pwd)
              if it would otherwise be treated as magic.  */
           handler = Ffind_file_name_handler (found, Qt);
           if (! NILP (handler))
-            found = concat2 (build_local_string ("/:"), found);
+            found = concat2 (SCOPED_STRING ("/:"), found);
           Vinvocation_directory = Ffile_name_directory (found);
         }
     }
@@ -2323,7 +2323,7 @@ decode_env_path (const char *evarname, const char *defalt, bool empty)
             }
 
           if (! NILP (tem))
-            element = concat2 (build_local_string ("/:"), element);
+            element = concat2 (SCOPED_STRING ("/:"), element);
         } /* !NILP (element) */
 
       lpath = Fcons (element, lpath);